1. Field of Endeavor
The present invention relates to a method for switching over a gas turbine plant from gaseous fuel to liquid fuel and vice-versa.
In particular, methods embodying principles of the present invention may be implemented in gas turbine plants having at least two combustors, wherein the second combustor is fed with the flue gases from the first combustor.
In this respect, for example the gas turbine plant for implementing a method of the present invention may include sequential combustion gas turbine units, i.e., gas turbine units having in series a compressor, a first combustor, a high pressure turbine, a second combustor fed with the flue gases of the first combustor, and a low pressure turbine.
Alternatively, a method of the invention may also be implemented in gas turbine plants having superimposed gas turbine units, i.e., a first gas turbine unit having in series a compressor, a first combustor, and a high pressure turbine and a second gas turbine unit fed with the flue gases of the first gas turbine unit having a compressor, a second combustor, and a low pressure turbine.
Naturally also gas turbine plants with sequential combustion gas turbine units together with gas turbine units are possible.
For sake of simplicity in the following, reference to a sequential combustion gas turbine will be made; it is anyhow clear that the same considerations apply to gas turbine plans made of superimposed (sequential) gas turbine units.
2. Brief Description of the Related Art
Switching over a sequential combustion gas turbine is a very delicate and complicated operation, since modification of the operating conditions of one combustor influences the operating conditions of the other combustor and, in addition, the stringent restrictions imposed by the emission limits (CO, UHC, and NOx emissions), flame temperature, and flame stability must be respected.
For these reasons, traditionally switch over from gas fuel operation to liquid fuel operation or vice-versa of a gas turbine plant operation is carried out by de-loading the gas turbine plant, thus switching off the second combustor, then switching over the first combustor and finally reigniting (with a different fuel) also the second combustor and loading up again the gas turbine plant.
Nevertheless, this traditional switch over method, that requires de-loading and re-loading of the gas turbine plant may adversely influence the final load, such as an electric generator, because during switch over no electric power or a reduced amount of electric power may be generated.
In addition, the large number of actions required for fuel switching over subjects the gas turbine plants (and in particular the first and second combustors) to temperature and load swings that adversely affect their lifetime.